The invention relates to a method for controlling magnetic recording in a magnetic recording medium, and a control device for magnetic recording, which can be used in particular with magnetic transfer technology for recording magnetization in perpendicular to the recording surface of the magnetic recording medium (the so-called perpendicular magnetic recording medium).
A first example of a conventional magnetic transfer technology will be explained with reference to FIG. 15(a) through FIG. 16(b), which explain the principle of magnetic transfer technology which performs magnetic transfer onto the recording surface of a magnetic recording medium. FIG. 15(a) is a cross-sectional view for explaining the initial magnetization of the so-called longitudinal magnetic recording medium, in which the magnetization thereof is parallel to the recording surface thereof. FIG. 15(b) is another cross-sectional view for explaining the transfer magnetization of the longitudinal magnetic recording medium.
As shown in FIG. 15(a), a magnetic recording disc 2 is positioned, as a longitudinal magnetic recording medium on a rotatable spindle stage 6. A ring head 3, including a magnet 3a and yokes 3b, is positioned at a position spaced apart for a distance Di in the upward direction from the recording surface of the magnetic recording disc 2. Further, a master disc 5 having a plurality of soft magnetic patterns 5a is placed above the recording surface of the magnetic recording disc 2. The ring head 3 generates a magnetic field in parallel to the circumferential direction of the magnetic recording disc 2 (that is, the parallel direction X). The direction of the magnetic field applied in the initial magnetization process and the direction of the magnetic field applied in the transfer magnetization process are opposite to each other.
For recording onto the longitudinal magnetic recording medium, first the magnetic recording medium is magnetized, as shown in FIG. 15(a), in one direction within the recording surface of the magnetic recording medium using the ring head 3 (initial magnetization). Then, as shown in FIG. 15(b), the ring head 3 is made to approach the magnetic recording disc 2 from the distance Di to the distance Dp, and a magnetic field, in the direction opposite the initial magnetization, is applied to the master disc 5 and magnetic recording disc 2, which are in close contact with each other.
The magnetic field generated by the ring head 3 cannot reverse the initial magnetization of the recording medium, since the magnetic field localizes to the soft magnetic patterns 5a with high magnetic permeability. However, the magnetic field generated by the ring head 3 causes a leakage magnetic field in the portions of the magnetic recording medium not facing to any soft magnetic layer, and the leakage magnetic field reverses the initial magnetization of the magnetic recording medium. In this way, the soft magnetic pattern 5a of the master disc 5 is recorded as a magnetization pattern, the direction thereof is opposite to the direction of the initial magnetization in the longitudinal direction (that is, the parallel direction X). Due to the principle explained above, it is necessary that the direction of the applied magnetic field applied in the initial magnetization process and the direction of the applied magnetic field applied in the transfer magnetization process for longitudinal magnetic recording media be opposite to each other.
FIG. 16(a) is a cross-sectional view for explaining the initial magnetization of the so-called perpendicular magnetic recording medium, in which the magnetization thereof is perpendicular to (in the perpendicular direction Y of) the recording surface thereof. FIG. 16(b) is another cross-sectional view for explaining the transfer magnetization of the perpendicular magnetic recording medium. In the method of magnetic transfer to the perpendicular magnetic recording media, the direction of the applied magnetic field merely changes from the foregoing parallel direction X to the perpendicular direction Y. The direction of the applied magnetic field applied in initial magnetization and the direction of the applied magnetic field applied in transfer magnetization are opposite to each other. Further, due to a principle similar to the principle of the method of magnetic transfer to the longitudinal magnetic recording medium, it is necessary that the directions of the applied magnetic fields applied in the initial magnetization process and in the transfer magnetization process be opposite to each other.
A second example of the conventional art is explained with reference to FIG. 17(a) through FIG. 18(b). FIG. 17(a) is a cross-sectional view for explaining the process of initial magnetization of the magnetic recording disc 2. FIG. 17(b) is another cross-sectional view for explaining the process of initial magnetization of the magnetic recording disc 2.
In FIG. 17(a), two single-pole heads (permanent magnets) 1 are aligned in perpendicular to (in the perpendicular direction Y of) the magnetic recording disc 2 and positioned symmetrically with respect to the magnetic recording disc 2. The magnetic recording disc 2, vacuum-chucked to the spindle stage 6, is inserted such that the surface of the magnetic recording disc 2, on which magnetic transfer is performed, coincides with the symmetry plane 0 spaced apart for an equal distance D from each of the magnetic poles of the two single-pole heads 1. The magnitude of the perpendicular component of the magnetic field created in the symmetry plane by the two single-pole heads 1 is several Oe, which is substantially small compared with the coercive force Hc of the magnetic recording media currently in use (around 3000 Oe). The distance D at this stage is from 5 to 10 cm.
In FIG. 17(b), the pair of single-pole heads 1 which are spaced apart from the magnetic recording medium for the distance D in FIG. 17(a) are made to approach the recording medium, while maintaining a symmetrical arrangement with respect to the symmetry plane at which the recording surface of the recording medium is positioned, until the distance to the recording medium is Di. Then, the entire surface of the magnetic recording disc 2 is magnetized in a single direction (perpendicular to the symmetry plane) by rotating the spindle stage 6. At this stage, the distance Di is from 2 mm to 3 mm, and the magnitude of the perpendicular component (perpendicular to the recording surface) of the magnetic field applied to the magnetic recording disc 2 is from 5000 to 6000 Oe.
FIG. 18(a) is a cross-sectional view for explaining the process of transfer magnetization of the magnetic recording medium 2. FIG. 18(b) is another cross-sectional view for explaining the process of transfer magnetization of the magnetic recording medium 2. In FIG. 18(a), the magnetic recording disc 2 vacuum-chucked to a spindle stage 6 is inserted between two ring heads 3, such that the surface, on which magnetic transfer is performed, of the magnetic recording disc 2 coincides with the symmetry plane 0 which is spaced apart for an equal distance D from the gaps of the two symmetrically positioned ring heads (permanent magnets) 3. Then, a master disc 5 is placed in close contact with the magnetic recording disc 2. At this stage, since the magnitude of the perpendicular component or of the parallel component of the magnetic field created at the symmetry plane by the two ring heads 3 is several Oe, which is small compared with the coercive force Hc of the magnetic recording media currently in use (around 3000 Oe), magnetic transfer is not conducted yet. The distance D at this stage is in the range between 5 and 10 cm like that shown in FIG. 17(a).
In FIG. 18(a), the pair of ring heads 3, spaced apart for the distance D from the magnetic recording medium, are made to approach the magnetic recording medium, while maintaining a symmetrical arrangement with respect to the symmetry plane at which the recording surface of the recording medium is positioned, until the distance to the recording medium is Dp. Then, the spindle stage 6 is rotated, resulting in magnetic transfer to the entire surface of the magnetic recording disc 2. The distance Dp at this stage is from 3 mm to 5 mm.
FIG. 19 and FIG. 20 show the magnetic field distribution in the surface of the magnetic recording medium immediately below the soft magnetic patterns 5a when a magnetic field is applied in the parallel direction X of the soft magnetic patterns 5a embedded in the master disc 5 using a ring head 3.
FIG. 19 shows the distribution of the parallel component of the magnetic field. The magnetic transfer to the longitudinal magnetic recording medium described with reference to FIG. 15(b), is performed utilizing the parallel component of the magnetic field in FIG. 19. In FIG. 19, the magnitude of the magnetic field is everywhere positive, and the parallel component is directed in only one direction. For this reason, the direction of the initial magnetization of the longitudinal magnetic recording media described above must be in the direction opposite the transfer magnetization.
However, a problem exists with respect to magnetization in the perpendicular direction Y. FIG. 20 shows the distribution of the perpendicular component of the magnetic field. Considering the distribution of the perpendicular component of the magnetic field with reference to FIG. 20, the direction of the perpendicular component has peaks in two directions, positive and negative, over one cycle of the soft magnetic pattern 5a. Hence this indicates that, even if the magnetic recording medium is not initially magnetized in advance in one direction (even if the medium is not magnetized in advance in a specific direction), the soft magnetic patterns 5a can be transferred.
FIG. 21 shows the waveform of the transferred signal 8 read out after performing only the transfer magnetization described with reference to FIGS. 18(a) and 18(b), without placing the recording medium in a particularly strong magnetic field after forming the recording layer of the magnetic recording medium by sputtering. The upward-directed transferred signal intensity Da and the downward-directed transferred signal intensity Db are equal, and it is seen that a symmetrical transferred signal 8 is obtained. That is, according to the transfer method described with reference to FIGS. 18(a) and 18(b), it is not necessary to initially magnetize the recording medium in advance in one direction.
On the other hand, FIG. 22 shows the transferred signal 8 transferred by the transfer magnetization described with reference to FIGS. 18(a) and 18(b) to the magnetic recording medium, first initialized by the initial magnetization process described with reference to FIGS. 17(a) and 17(b) such that the initial magnetization is perpendicular to the magnetic recording medium. As is seen from FIG. 22, the waveform of the transferred signal 8 is asymmetric, with the transferred signal intensities such that Da less than Db. The reason that a waveform in which the transferred signal intensities Da and Db are equal is not obtained is considered in the following way. Since the magnetic recording medium is magnetized in one of the directions in advance by the initial magnetization of FIGS. 17(a) and 17(b), it is difficult to make the magnitudes of the recorded upward-directed magnetization and downward-directed magnetization equal, even if a magnetic field equal in magnitude and opposite in direction like that shown in FIG. 20 is applied in the transfer magnetization process of FIGS. 18(a) and 18(b). If the asymmetrical relation of the transferred signal intensities, Da less than Db, in the transfer magnetization process is left unaltered, there is the problem that normal recording cannot be performed in the process of transfer magnetization.
In view of the foregoing, it would be desirable to provide a method for controlling magnetic recording in a magnetic recording medium, and a control device for magnetic recording, which are capable of obtaining a symmetrical transferred signal waveforms equal in magnitude with good reproducibility, and of performing magnetic transfer with high reliability.
According to an aspect of the invention, a method of controlling magnetic recording in a magnetic recording medium is provided, wherein the method includes initial magnetization prior to magnetically performing transfer magnetization on the magnetic recording layer of the magnetic recording medium; the method including: a step of demagnetizing; the step of demagnetizing including applying an alternating magnetic field, the polarity thereof changing, in perpendicular to or both in perpendicular and parallel to the recording surface of the magnetic recording layer; and decreasing the intensity of the alternating magnetic field gradually with elapse of time to demagnetize the entire magnetic recording layer.
Advantageously, the step of demagnetizing employs an electromagnet generating the alternating magnetic field, the polarity thereof changing with elapse of time in a predetermined position to demagnetize the entire magnetic recording layer.
Advantageously, the step of demagnetizing employs a magnetic head including a plurality of mutually separated permanent magnets embedded in a nonmagnetic base, the magnetic head generating an alternating magnetic field, the alternating magnetic field being constant in time, the polarity of the alternating magnetic field changing spatially to demagnetize the entire magnetic recording layer.
Advantageously, the alternating magnetic field is generated by moving the magnetic head in perpendicular to the recording surface of the magnetic recording medium.
Advantageously, the alternating magnetic field is generated by moving the magnetic head in a direction which traverses the magnetic recording medium, while the distance between the magnetic head and the recording surface of the magnetic recording medium is held constant.
Advantageously, the magnetic recording medium is a perpendicular magnetic medium having an easy axis of magnetization in the direction perpendicular to the recording surface. Advantageously, the direction of the magnetization recorded in the magnetic recording medium is perpendicular to the recording surface.
Advantageously, the magnitude of the applied alternating magnetic field first saturates, and then decreases with the polarity thereof changing sinusoidally with time as described by the following equation.
H(t)=A0g(t)cos(2xcfx80f.t),
where t is the time, A0 is the maximum applied magnetic field, and f is the frequency.
Advantageously, the method further includes a step of transfer magnetization performed after the step of demagnetizing, the step of transfer magnetization including preparing a master disc including a nonmagnetic substrate and soft magnetic layers of a soft magnetic material embedded in the nonmagnetic substrate such that the soft magnetic layers are isolated from each other and aligned periodically; positioning the master disc in close contact with or in close proximity to the recording surface of the magnetic recording layer of the magnetic recording medium; and applying a magnetic field in parallel to the recording surface in close contact with or in close proximity to the master disc to magnetically transferring the servo data stored in the master disc in the form of the soft magnetic patterns to the magnetic recording medium.
According to another aspect of the invention, there is provided a control device for controlling magnetic recording, the control device including: a demagnetization means and a transfer means; the demagnetization means applying an alternating magnetic field in perpendicular to or in perpendicular and parallel to the recording surface of the magnetic recording layer of a magnetic recording medium, the intensity of the alternating magnetic field decreasing with elapse of time to initially demagnetize the entire of the magnetic recording layer; the magnetic transfer means positioning a master disc in close contact with or in close proximity to the recording surface of the magnetic recording layer, the master disc including a nonmagnetic substrate and a plurality of soft magnetic layers of a soft magnetic material embedded in the nonmagnetic substrate such that the soft magnetic layers are isolated from each other and aligned periodically; and the magnetic transfer means applying a magnetic field in parallel to the recording surface of the magnetic recording layer to magnetically transfer the servo data stored in the master disc in the form of the soft magnetic patterns to the magnetic recording medium initially demagnetized by the demagnetization means.